Bis-imine pyridine complex of lanthanides catalytic system comprising said bis-imine pyridine complex and process for the (co)polymerization of conjugated dienes

ABSTRACT

A bis-imine pyridine complex of lanthanides having general formula (I): Said bis-imine pyridine complex of lanthanides having general formula (I) can be advantageously used in a catalytic system for the (co)polymerization of conjugated dienes.

The present invention relates to a bis-imine pyridine complex of lanthanides.

More specifically, the present invention relates to a bis-imine pyridine complex of lanthanides and its use in a catalytic system for the (co)polymerization of conjugated dienes.

The present invention also relates to a catalytic system for the (co)polymerization of conjugated dienes comprising said bis-imine pyridine complex of lanthanides.

Furthermore, the present invention relates to a (co)polymerization process of conjugated dienes, in particular a process for the polymerization of 1,3-butadiene or isoprene, characterized in that it uses said catalytic system.

It is known that the stereospecific (co)polymerization of conjugated dienes is an extremely important process in the chemical industry for obtaining products which are among the most widely-used rubbers.

It is known, for example, that polybutadiene 1,4-cis is a synthetic elastomer whose properties are very similar to those of natural rubber. Since the beginning of stereospecific polymerization, numerous catalytic systems have been used for the production of this elastomer, as described, for example, by Porri L. et al. in: “Comprehensive Polymer Science” (1989), Eastmond G. C. et al. Eds., Pergamon Press, Oxford, UK, Vol. 4, Part II, pages 53-108.

A first catalytic system capable of giving a polybutadiene having a 1,4-trans content ranging from 70% to 90% is described in U.S. Pat. No. 3,050,513 and was based on titanium compounds containing iodine, such as titanium tetraiodide (TiI₄), combined with an aluminium hydride such as, for example, lithium-aluminium hydride, sodium-aluminium hydride, potassium-aluminium hydride, rubidium-aluminium hydride, caesium-aluminium hydride.

Efforts were then made in the art to find catalytic systems capable of giving polybutadiene having a high content of 1,4-cis units.

Catalytic systems capable of giving a polybutadiene having a 1,4-cis content equal to about 93% are described, for example, by W. Cooper in “The Stereo Rubbers” (1977), Ed. W. M. Saltman, Wiley, New York, page (catalytic system: AliBu₃-TiI₄); W. Marconi et al., in “Chimica Industriale” (1963), Vol. 45, page 522 (catalytic system: AlEt₃-AlEt₂I—TiCl₄); W. Marconi et al., in “Journal of Polymer Science” (1965), Part A, Vol. 3, page 735 (catalytic system: AlHCl₂.OEt₂-TiCl₄—AlI₃).

The formation of catalytic systems characterized by a higher stereospecificity capable of giving polybutadiene having a content of 1,4-cis units equal to about 96%, is described, for example: with respect to catalytic systems comprising cobalt, in Italian patent IT 592,477 and by Gippin M. et al. in “Industrial & Engineering Chemistry, Product Research and Development” (1962), Vol. 1(1), pages 32-39; with respect to catalytic systems comprising nickel, by Ueda et. al., in “Koogyo Kagaku Zasshi” (1963), Vol. 66, page 1103, and by Throckmorton et al. in “Rubber Chemistry and Technology” (1972), Vol. 45, pages 268-277.

Some works relating to the use of catalytic systems comprising lanthanides for the 1,4-cis polymerization of conjugated dienes were published in the first half of the sixties'.

Saltman et al. in “Rubber Chemistry and Technology” (1973), Vol. 46, page 1055 and Throckmorton et al. in “Kautschuk and Gummi Kunstoffe” (1969), Vol. 22, page 293, for example, describe the use of catalytic systems comprising cerium. These catalytic systems, however, were soon abandoned as a result of the metal residues remaining in the polymer which caused an oxidation of the polymer itself.

The use of catalytic systems comprising lanthanides such as, for example, neodymium, praseodymium and gadolinium, is also known, as described, for example, by: Hsieh H. L. et al. in “Rubber Chemistry and Technology” (1985), Vol. 58(1), pages 117-145. The polybutadiene obtained using these catalytic systems has a content of 1,4-cis units of about 98%, a good processability, and a relatively large molecular weight distribution.

The use is also known of catalytic systems comprising uranium allyls capable of providing a polybutadiene having a very high content of 1,4-cis units (i.e. 99%) as described, for example, by Lugli et al. in “Die Makromoleculare Chemie” (1974), Vol. 175, Issue 7, pages 2021-2027; De Chirico A. et al. in “Die Makromoleculare Chemie” (1974), Vol. 175, Issue 7, pages 2029-2038; Bruzzone M. et al. in “Rubber Chemistry and Technology” (1974), Vol. 47, page 1175; Mazzei A. in “Die Makromoleculare Chemie” (1981), Vol. 4, Issue Supplement 3, pages 61-72. These catalytic systems, however, were also abandoned due to the presence of radioactive residues in the polymers obtained.

From the above documents it emerges, however, that the use of catalytic systems comprising lanthanides offered advantages with respect to the use of catalysts based on titanium, cobalt and nickel, previously proposed and in use at that time. In particular, catalytic systems comprising lanthanides, as mentioned above, were capable of giving polymers, in particular polybutadiene, having a higher content of 1,4-cis units 97%), with a more linear structure and, consequently, more suitable for the production of tyres, which represents the most important application (about 80%) of polybutadiene 1,4-cis use. Furthermore, the above catalytic systems comprising lanthanides did not have a cationic activity and proved to have a higher activity when used in solution polymerization in the presence of aliphatic solvents rather than aromatic solvents, as described, for example, by Ricci G. et al., in “Die Makromoleculare Chemie”, Rapid Communications, (1986), Vol. 7, page 335.

Further studies were then carried out with the aim of finding new catalytic systems comprising lanthanides and/or of improving the catalytic activity of already known catalytic systems.

In particular, studies were mainly carried out on catalytic systems comprising neodymium as these catalytic systems had a higher catalytic activity with respect to catalytic systems comprising other lanthanides and they were capable of providing polymers which, after vulcanization, had a higher resistance to aging with respect to the polymers obtained with catalytic systems comprising titanium, cobalt and nickel. Furthermore, these studies were also supported by the great availability, at a low price, of the precursors, including neodymium.

European patent EP 0 076 535, for example, describes an enhanced process for the (co)polymerization of conjugated diolefins comprising the use of a particular catalytic system including at least one compound of a metal selected from those of Group III B of the Periodic System having an atomic number between 21 and 103, preferably neodymium, a derivative of an organic halide and an organometallic compound containing aluminium such as, for example, alkyl aluminium hydride, or trialkyl aluminium hydride. Said process allows (co)polymers having a high content of 1,4-cis units (>98%) and a high linearity, to be obtained.

U.S. Pat. No. 4,242,232 describes a catalyst comprising (a) a reaction mixture formed by reacting a carboxylate of a metal having an atomic number ranging from 57 to 71 such as, for example, lanthanum, cerium, praseodymium, neodymium with an aluminium tri-alkyl, (b) an aluminium alkyl and/or an aluminium alkyl hydride and (c) a Lewis acid. The polybutadiene obtained by using said catalyst has a content of 1,4-cis ranging from 80 to 99%.

In their simplest form, the catalytic systems comprising neodymium are obtained by reaction between neodymium trichloride, as such or complexed with donors (e.g. alcohols, ethers, tri-butyl-phosphate, alkylsulfoxides, amides, pyridine), and an aluminium tri-alkyl (e.g. aluminium tri-iso-butyl, aluminium tri-ethyl, aluminium tri-methyl): in this case, these are binary catalytic systems. Said binary catalytic systems are described, for example, by Yang J. H. et al., in “Macromolecules” (1982), Vol. 15(2), pages 230-233; Porri L. et al. in “Macromolecular Symposia” (1998), Vol. 128, Issue 1, pages 53-61.

Alternatively, neodymium chloride can be obtained by reaction of a neodymium compound (e.g., alcoholate, carboxylate) with a chlorine donor (e.g., di-ethyl aluminium chloride, ethyl-aluminium dichloride, bisaluminium tri-ethyl trichloride, t-butyl chloride) and then reacted with an aluminium alkyl or an aluminium tri-alkyl: in this case, these are tertiary catalytic systems. Said tertiary catalytic systems are described, for example, by: Cabassi F. et al. in “Transition Metal Catalyzed Polymerizations” (1988), Quirk R. P. Ed., Cambridge University Press, MA, USA, pages 655-670; Ricci G. et al. in “Polymer Communications Guilford” (1987), Vol. 28, Issue 8, pages 223-226; or in Italian patent IT 1,197,465.

The order for adding the components (chlorine donor, aluminium alkyl or aluminium tri-alkyl) to the neodymium compound can be extremely important for the nature of the catalytic system to be obtained. By first adding aluminium alkyl hydride or aluminium tri-alkyl and only subsequently the chlorine donor, in fact, homogeneous catalysts are obtained; vice versa, when the chlorine donor is added before the aluminium alkyl hydride or the aluminium tri-alkyl, heterogeneous systems are obtained, as described, for example, by Porri et al. in “ACS Symposium Series” (2000), Vol. 749, Chapter 2, pages 15-30. The order of adding the above-mentioned components, is also decisive for the catalytic activity and for the polydispersity of the resulting polymers.

In the binary and ternary catalytic systems mentioned above, however, the percentage of neodymium catalytically active is relatively low, normally ranging from 7% to 8% (said percentage referring to the molar percentage of active neodymium with respect to the total moles of neodymium charged), as described, for example, by Marina N. G. et al., in “Doklady Akademii Nauk SSSR” (1982), Vol. 265, pages 1431-1433.

Much more active ternary catalytic systems, containing a higher percentage of catalytically active neodymium, have been obtained by reaction between allyl compounds of neodymium, obtained by reaction between the complex of neodymium chloride with tetrahydrofuran (THF) and allyl Grignard, and aluminium alkyl [e.g. aluminium trialkyl, methylaluminoxane (MAO), tetra-isobutyl-aluminoxane (TIBAO)], as described, for example, in Italian patent IT 1,228,442; or by: Porri L. et al. in “Macromolecular Symposia” (1993), Vol. 66, pages 231-244; Porri L. et al. in “Polymer Preprints”, “American Chemical Society Division Polymer Chemistry” (1998), Vol. 39, pages 214-215; Porri L. in “Recent developments in Lanthanide catalysts for 1,3-diene polymerization”, in “ACS Symposium Series 749—Olefin Polymerization: Emerging Frontiers” (2000), P. Arjunan, J. C. McGrath and T. Hanlon Eds., Oxford University Press, USA, pages 15-30. Said ternary catalytic systems provide a polybutadiene having a much lower polydispersity than those obtained by means of the classical ternary catalytic systems mentioned above. Furthermore, said ternary catalytic systems can also produce polyisoprene and/or other polymers deriving from the (co)polymerization of substituted butadienes, providing (co)polymers with a high content of 1,4-cis units (i.e. content≧90%). In particular, a polymer is obtained from the polymerization of isoprene, having a content of 1,4-cis units equal to about 94%, which can be advantageously used for producing elastomeric blends for the production of tyres.

As mentioned above, due to the fact that the (co)polymers of conjugated dienes, in particular polybutadiene and polyisoprene, with a high content of 1,4-cis units, are the most widely used on an industrial scale, in particular for the production of tyres, the study of new catalytic systems capable of providing said (co)polymers, is still of great interest.

The Applicant has faced the problem of finding a new bis-imine pyridine complex of lanthanides that can be used in a catalytic system capable of providing (co)polymers of conjugated dienes, in particular polybutadiene and polyisoprene, linear or branched, with a high content of 1,4-cis units, i.e. a content of 1,4-cis units 99% in the case of polybutadiene, and 98% in the case of polyisoprene. Furthermore, said polyisoprene has a glass transition temperature (TO similar to that of natural rubber.

An object of the present invention therefore relates to a bis-imine pyridine complex of lanthanides having general formula (I):

wherein:

-   -   Ln represents a metal of the series of lanthanides, preferably         selected from neodymium (Nd), lanthanum (La), praseodymium (Pr),         gadolinium (Gd), europium (Eu), terbium (Tb), samarium (Sm),         erbium (Er), ytterbium (Yb);     -   R₁ and R₂, equal to or different from each other, represent a         hydrogen atom; or they are selected from linear or branched         C₁-C₂₀, preferably C₁-C₁₅, alkyl groups, cycloalkyl groups         optionally substituted, aryl groups optionally substituted;     -   R₃ and R₄, equal to or different from each other, represent a         hydrogen atom; or they are selected from linear or branched         C₁-C₂₀, preferably C₁-C₁₅, alkyl groups, cycloalkyl groups         optionally substituted, aryl groups optionally substituted;     -   or R₂ and R₄ can be optionally bound to each other so as to         form, together with the other atoms to which they are bound, a         saturated, unsaturated or aromatic cycle containing from 3 to 6         carbon atoms, optionally substituted with linear or branched         C₁-C₂₀, preferably C₁-C₁₅, alkyl groups, said cycle optionally         containing other heteroatoms such as, for example, oxygen,         sulfur, nitrogen, silicon, phosphorous, selenium;     -   or R₁ and R₃ can be optionally bound to each other so as to         form, together with the other atoms to which they are bound, a         saturated, unsaturated or aromatic cycle containing from 3 to 6         carbon atoms, optionally substituted with linear or branched         C₁-C₂₀, preferably C₁-C₁₅, alkyl groups, said cycle optionally         containing other heteroatoms such as, for example, oxygen,         sulfur, nitrogen, silicon, phosphorous, selenium;     -   X₁, X₂ and X₃, equal to or different from each other, represent         a halogen atom such as chlorine, bromine, iodine; or they are         selected from linear or branched C₁-C₂₀, preferably C₁-C₁₅,         alkyl groups, —OCOR₅ or —OR₅ groups wherein R₅ is selected from         linear or branched C₁-C₂₀, preferably C₁-C₁₅, alkyl groups.

For the aim of the present description and of the following claims, the definitions of the numerical intervals always include the extremes, unless otherwise specified

For the aim of the present description and of the following claims, the term “metal belonging to the family of lanthanides” means any metal belonging to the Periodic Table of Elements having an atomic number ranging from 57 to 71.

It should be noted that, for the aim of the present invention and of the following claims, the term “Periodic Table of the Elements” refers to the IUPAC version of the “Periodic Table of the Elements” dated Jun. 22, 2007, provided in the following Internet website www.iupac.org/reports/periodic_table.

The term “C₁-C₂₀ alkyl groups” refers to linear or branched alkyl groups having from 1 to 20 carbon atoms. Specific examples of C₁-C₂₀ alkyl groups are: methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nnonyl, n-decyl, 2-butyloctyl, 5-methylhexyl, 4-ethylhexyl, 2-ethylheptyl, 2-ethylhexyl.

The term “cycloalkyl groups” refers to cycloalkyl groups having from 3 to 30 carbon atoms. Said cycloalkyl groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of cycloalkyl groups are: cyclopropyl, 2,2-difluorocyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, hexamethylcyclohexyl, pentamethylcyclopentyl, 2-cyclooctylethyl, methylcyclohexyl, methoxycyclohexyl, fluorocyclohexyl, phenylcyclohexyl.

The term “aryl groups” means aromatic carbocyclic groups. Said aromatic carbocyclic groups can be optionally substituted with one or more groups, equal to or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups, cyano groups; amino groups; nitro groups. Specific examples of aryl groups are: phenyl, methylphenyl, trimethylphenyl, methoxyphenyl, hydroxyphenyl, phenyloxyphenyl, fluorophenyl, pentafluorophenyl, chlorophenyl, bromophenyl, nitrophenyl, dimethylaminophenyl, naphthyl, phenylnaphthyl, phenanthrene, anthracene.

The term “cyclo” relates to a system containing a ring containing from 3 to 6 carbon atoms, optionally also containing, in addition to the nitrogen atom, other heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorous. Specific examples of cyclo are: pyridine, thiadiazole.

According to a preferred embodiment of the present invention, in said bis-imine pyridine complex of lanthanides having general formula (I):

-   -   Ln is neodymium (Nd), praseodymium (Pr), gadolinium (Gd),         lanthanum (La), preferably neodymium (Nd);     -   R₁ and R₂, the same as each other, are a hydrogen atom; or they         are selected from linear or branched C₁-C₂₀ alkyl groups, and         are preferably a methyl group; or they are selected from         cycloalkyl groups optionally substituted;     -   R₃ and R₄, equal to or different from each other, are selected         from phenyl groups optionally substituted; or they are selected         from cycloalkyl groups optionally substituted;     -   X₁, X₂ and X₃, the same as each other, represent a halogen atom         such as chlorine, bromine, iodine, preferably chlorine.

The bis-imine pyridine complex of lanthanides having general formula (I) is intended, according to the present invention, as being in any physical form such as, for example, isolated and purified solid form, solvated form with a suitable solvent, or supported on suitable organic or inorganic solids, preferably having a physical granular or powder form.

The bis-imine pyridine complex of lanthanides having general formula (I) is prepared starting from ligands known in the art.

Specific examples of ligands which can be used for the aim of the present invention are those having the following formulae (L1)-(L8):

Said ligands having formulae (L1)-(L8), can be prepared by means of processes known in the art. Said ligands having formulae (L1)-(L8) can be prepared, for example, by means of condensation reactions between primary amines and diketones as described, for example, in International patent applications WO 2002/10133 and WO 2002/34701.

The bis-imine pyridine complex of lanthanides having general formula (I) can be prepared according to processes known in the art for the preparation of analogous complexes of other metals such as, for example, cobalt, nickel. Said bis-imine pyridine complex of lanthanides can be prepared, for example, by reaction between compounds of lanthanides having general formula Ln(X)₃ wherein Ln and X have the same meanings described above, as such or complexed with ethers [for example, diethyleter, tetrahydrofuran (THF), dimethoxyethane], with ligands having formulae (L1)-(L8) indicated above, in a molar ratio ligand (L)/lanthanide (Ln) ranging from 1 to 1.5, preferably operating in the presence of at least one ether solvent [for example, tetrahydrofuran (THF)], at room temperature or higher. The bis-imine pyridine complex of lanthanides thus obtained can be subsequently recovered by means of methods known in the art such as, for example, precipitation by means of a non-solvent (for example pentane), followed by separation by filtration or decanting and optional subsequent solubilization in a suitable solvent followed by low-temperature crystallization.

For the aim of the present description and of the following claims, the phrase “room temperature” means a temperature ranging from 20° C. to 25° C.

As specified above, the present invention also relates to a catalytic system for the (co)polymerization of conjugated dienes comprising said bis-imine pyridine complex of lanthanides having general formula (I).

A further object of the present invention therefore relates to a catalytic system for the (co)polymerization of conjugated dienes comprising:

-   (a) at least one bis-imine pyridine complex of lanthanides having     general formula (I); -   (b) at least one co-catalyst selected from:     -   (b₁) aluminium alkyls having general formula (II):

Al(X′)_(n)(R₆)_(3-n)  (II)

-   -    wherein X′ represents a halogen atom such as, for example,         chlorine, bromine, iodine, fluorine; R₆ is selected from linear         or branched C₁-C₂₀ alkyl groups, C₃-C₂₀ cycloalkyl groups, aryl         groups, said groups being optionally substituted with one or         more silicon or germanium atoms; and n is an integer ranging         from 0 to 2; (b₂) aluminoxanes having general formula (III):

(R₇)₂—Al—O—[—Al(R₈)—O—]_(p)—Al—(R₉)₂  (III)

-   -    wherein R₇, R₈ and R₉, equal to or different from each other,         represent a hydrogen atom, a halogen atom such as, for example,         chlorine, bromine, iodine, fluorine; or they are selected from         linear or branched C₁-C₂₀ alkyl groups, C₃-C₂₀ cycloalkyl         groups, aryl groups, said groups being optionally substituted         with one or more silicon or germanium atoms; and p is an integer         ranging from 0 to 1000;     -   (b₃) compounds having general formula (IV):

D⁺E⁻  (IV)

-   -    wherein D⁺ represents a Brønsted acid capable of donating a         proton and of reacting irreversibly with the substituent X of         the bis-imine pyridine complex of lanthanides having general         formula (I); E⁻ represents a compatible anion capable of         stabilizing the active catalytic species which are generated by         the reaction of the two components and which is sufficiently         labile as to be able to be removed by an olefinic monomer,         preferably a boron atom, even more preferably an anion having         formula B(Ar)₄ ⁽⁻⁾ wherein the substituents Ar, equal to or         different from each other, are selected from aryl groups such         as, for example, phenyl, pentafluorophenyl,         bis(trifluoromethyl)phenyl.

Specific examples of aluminium alkyls (b₁) which are particularly useful for the aim of the present invention are: tri-methyl-aluminium, tri-(2,3,3-tri-methyl-butyl)-aluminium, tri-(2,3-di-methyl-hexyl)aluminium, tri-(2,3-di-methyl-butyl)-aluminium, tri(2,3-di-methyl-pentyl)-aluminium, tri-(2,3-di-methylheptyl)-aluminium, tri-(2-methyl-3-ethyl-pentyl)aluminium, tri-(2-methyl-3-ethyl-hexyl)-aluminium, tri(2-methyl-3-ethyl-heptyl)-aluminium, tri-(2-methyl-3-propyl-hexyl)-aluminium, tri-ethyl-aluminium, tri-(2-ethyl-3-methyl-butyl)-aluminium, tri-(2-ethyl-3-methylpentyl)-aluminium, tri-(2,3-di-ethyl-pentyl-aluminium), tri-n-propyl-aluminium, tri-iso-propyl-aluminium, tri(2-propyl-3-methyl-butyl)-aluminium, tri-(2-iso-propyl-3-methyl-butyl)-aluminium, tri-n-butyl-aluminium, triiso-butyl-aluminium (TIBA), tri-tert-butyl-aluminium, tri-(2-iso-butyl-3-methyl-pentyl)-aluminium, tri(2,3,3-tri-methyl-pentyl)-aluminium, tri-(2,3,3-trimethyl-hexyl)-aluminium, tri-(2-ethyl-3,3-di-methylbutyl)-aluminium, tri-(2-ethyl-3,3-di-methyl-pentyl)aluminium, tri-(2-iso-propyl-3,3-dimethyl-butyl)aluminium, tri-(2-tri-methylsilyl-propyl)-aluminium, tri-2-methyl-3-phenyl-butyl)-aluminium, tri-(2-ethyl-3-phenyl-butyl)-aluminium, tri-(2,3-di-methyl-3-phenylbutyl)-aluminium, tri-(2-phenyl-propyl)-aluminium, tri-[2-(4-fluoro-phenyl)-propyl]-aluminium, tri-[2-(4-chloro-phenyl)-propyl]-aluminium, tri-[2-(3-iso-propylphenyl-tri-(2-phenyl-butyl)-aluminium, tri-(3-methyl-2-phenyl-butyl)-aluminium, tri-(2-phenyl-pentyl)aluminium, tri-[2-(penta-fluoro-phenyl)-propyl]-aluminium, tri-(2,2-diphenyl-ethyl]-aluminium, tri-(2-phenyl-methyl-propyl)-aluminium, tri-pentyl-aluminium, tri-hexyl-aluminium, tri-cyclohexyl-aluminium, trioctyl-aluminium, di-ethyl-aluminium hydride, di-npropyl-aluminium hydride, di-n-butyl-aluminium hydride, di-iso-butyl-aluminium hydride (DIBAH), di-hexylaluminium hydride, di-iso-hexyl-aluminium hydride, dioctyl-aluminium hydride, di-iso-octyl-aluminium hydride, ethyl-aluminium di-hydride, n-propyl-aluminium di-hydride, iso-butyl-aluminium di-hydride, di-ethyl-aluminium chloride, mono-ethyl-aluminium dichloride, di-methyl-aluminium chloride, di-isobutyl-aluminium chloride, iso-butyl-aluminium dichloride, ethyl-aluminium sesquichloride, and also the corresponding compounds in which one of the hydrocarbon substituents is substituted with a hydrogen atom and those in which one or two of the hydrocarbon substituents are substituted with an iso-butyl group. Tri-iso-butyl-aluminium (TIBA), di-iso-butyl-aluminium hydride (DIBAH), are particularly preferred.

Specific examples of aluminoxanes (b₂) which are particularly useful for the aim of the present invention are: methylaluminoxane (MAO), ethyl-aluminoxane, n-butyl-aluminoxane, tetra-iso-butyl-aluminoxane (TIBAO), tert-butyl-aluminoxane, tetra-(2,4,4-tri-methylpentyl)-aluminoxane (TIOAO), tetra-(2,3-di-methylbutyl)-aluminoxane (TDMBAO), tetra-(2,3,3-tri-methylbutyl)-aluminoxane (TDMBAO). Methylaluminoxane (MAO), tetra-iso-butyl-aluminoxane (TIBAO), are particularly preferred. Said aluminoxanes can be prepared according to processes known in the art. Said aluminoxanes can be prepared, for example, by reacting at least one trialkyl-aluminium or at least one di-alkyl aluminium monochloride with water or with a salt containing crystallization water such as, for example, copper sulfate pentahydrate, aluminium sulfate hexadecahydrate, in the presence of at least one organic solvent such as, for example, benzene, toluene, xylene.

Specific examples of compounds (b₃) having general formula (IV) which are particularly useful for the aim of the present invention are: tetrakispentafluorophenyl-borate tributylammonium-tetrakispentafluorophenyl-aluminate, tributylammonium-tetrakis-[(3,5-di-(trifluorophenyl)]-borate, tributylammonium-tetrakis-(4-fluorophenyl)]-borate, N,N-dimethylbenzylammonium-tetrakis-pentafluorophenyl-borate, N,N-dimethyl-hexylammonium-tetrakis-pentafluorophenyl-borate, N,N-dimethylanilinium-tetrakis-(pentafluorophenyl)borate, N,N-dimethylanilinium-tetrakis(pentafluorophenyl)-aluminate, di-(propyl)-ammoniumtetrakis-(pentafluorophenyl)-borate, di-(cyclohexyl)ammonium-tetrakis-(pentafluorophenyl)-borate, triphenyl-carbenium-tetrakis-(pentafluorophenyl)-borate, tri-phenylcarbenium-tetrakis-(penta-fluorophenyl)aluminate. Tetrakis-pentafluorophenyl-borate is preferred.

Alternatively, the compounds (b₃) can be selected from compounds having formula B(Ar)₃ wherein Ar has the same meanings described above; or from compounds having formula B(Ar)₃P wherein Ar has the same meanings described above and P is a pyrrole radical optionally substituted.

Further details relating to aluminium alkyls (b₁), aluminoxanes (b₂) and compounds (b₂), can be found in international patent application WO 2011/061151.

For the aim of the present description and of the following claims, the term “moles” and “molar ratio” are used with reference to compounds consisting of molecules and also with reference to atoms and ions, omitting, for the latter, the terms gram atom or atomic ratio, even if scientifically more correct.

According to a preferred embodiment of the present invention, in said catalytic system, the molar ratio between the lanthanide present in the bis-imine pyridine complex of lanthanides (a) having general formula (I) and the aluminium present in the co-catalyst (b) selected from aluminium alkyls (b₁) or aluminoxanes (b₂), can range from 5 to 5,000, preferably from 10 to 1,000.

According to a preferred embodiment of the present invention, in said catalytic system, the molar ratio between the lanthanide present in the bis-imine pyridine complex of lanthanides (a) having general formula (I) and the boron present in the co-catalyst (b) selected from compounds (b₃) having general formula (IV), can range from 0.1 to 15, preferably from 0.5 to 10.

For the aim of the present invention, other additives or components can be optionally added to the above catalytic system in order to adapt it so as to satisfy specific practical requirements. The catalytic systems thus obtained should therefore be considered as being included in the scope of the present invention. Additives and/or components which can be added in the preparation and/or formulation of the catalytic system object of the present invention are, for example, inert solvents, such as, for example, aliphatic and/or aromatic hydrocarbons; aliphatic and/or aromatic ethers; weakly coordinating additives (e.g. Lewis bases) selected, for example, from non-polymerizable olefins; sterically hindered or electronically poor ethers; halogenating agents such as, for example, silicon halides, hydrogenated hydrocarbons, preferably chlorinated; or mixtures thereof.

Said catalytic system can be prepared according to methods known in the art.

Said catalytic system, for example, can be prepared separately (preformed) and subsequently introduced into the (co)polymerization environment. In this respect, said catalytic system can be prepared by reacting at least one bis-imine pyridine complex of lanthanides (a) having general formula (I) with at least one co-catalyst (b), optionally in the presence of other additives or components selected from those listed above, in the presence of a solvent such as, for example, toluene, heptane, at a temperature ranging from 20° C. to 60° C., for a time ranging from 10 seconds to 10 hours, preferably from 30 seconds to 5 hours. More details on the preparation of said catalytic system can be found in the examples provided hereunder.

Alternatively, said catalytic system can be prepared in situ, i.e. directly in the (co)polymerization environment. In this respect, said catalytic system can be prepared by introducing the bis-imine pyridine complex of lanthanides (a) having general formula (I), the co-catalyst (b) and the preselected conjugated diene(s) to be (co)polymerized, separately, operating under the conditions in which the (co)polymerization is carried out.

For the aim of the present invention, the above catalytic systems can also be supported on inert solids, preferably consisting of silicon and/or aluminium oxides, such as, for example, silica, alumina or silico-aluminates. The known supporting techniques can be used for supporting said catalytic systems, generally comprising the contact, in a suitable inert liquid medium, between the carrier, optionally activated by heating to temperatures higher than 200° C., and one or both of components (a) and (b) of the catalytic system object of the present invention. For the aim of the present invention, it is not necessary for both components to be supported, as the bis-imine pyridine complex of lanthanides (a) having general formula (I) only, or the co-catalyst (b) only, can be present on the surface of the carrier. In the latter case, the missing component on the surface is subsequently put in contact with the supported component, at the moment in which the catalyst active for the polymerization is to be formed.

The bis-imine pyridine complex of lanthanides having general formula (I), and the catalytic systems based thereon, which have been supported on a solid by the functionalization of the latter and the formation of a covalent bond between the solid and the bis-imine pyridine complex of lanthanides having general formula (I), are also included in the aim of the present invention.

The present invention also relates to a process for the (co)polymerization of conjugated dienes, characterized in that it uses said catalytic system.

The quantity of bis-imine pyridine complex of lanthanides (a) having general formula (I) and of co-catalyst (b) that can be used in the (co)polymerization of conjugated dienes varies according to the (co)polymerization process to be carried out. Said quantity is in any case such as to obtain a molar ratio between the lanthanide present in the bis-imine pyridine complex of lanthanides (a) having general formula (I) and the metal present in the co-catalyst (b), i.e. aluminium when the co-catalyst (b) is selected from aluminium alkyls (b₁) or aluminoxanes (b₂), boron when the co-catalyst (b) is selected from compounds (b₃) having general formula (IV), comprised within the values indicated above.

Specific examples of conjugated dienes which can be (co)polymerized using the catalytic system according to the present invention are: 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, cyclo-1,3-hexadiene. Preferred (co)polymerizable conjugated dienes are 1,3-butadiene, isoprene. The above (co)polymerizable conjugated dienes can be used alone, or in a mixture of two or more dienes. In the latter case, i.e. using a mixture of two or more dienes, a copolymer is obtained.

According to a particularly preferred embodiment, the present invention relates to a polymerization process of 1,3-butadiene or isoprene, characterized in that it uses said catalytic system.

Said (co)polymerization is generally carried out in the presence of a polymerization solvent generally selected from inert organic solvents such as, for example, saturated aliphatic hydrocarbons such as, for example, butane, pentane, hexane, heptane, or mixtures thereof; saturated cyclo-aliphatic hydrocarbons such as, for example, cyclopentane, cyclohexane, or mixtures thereof; mono-olefins such as, for example, 1-butene, 2-butene, or mixtures thereof; aromatic hydrocarbons such as, for example, benzene, toluene, xylene, or mixtures thereof; halogenated hydrocarbons such as, for example, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene, chlorotoluene, or mixtures thereof. The (co)polymerization solvent is preferably selected from saturated aliphatic hydrocarbons.

Alternatively, said (co)polymerization can be carried out using, as (co)polymerization solvent, the same conjugated diene(s) to be (co)polymerized, according to the process known as “bulk process”.

The concentration of conjugated diene to be (co)polymerized in said (co)polymerization solvent generally ranges from 5% by weight to 50% by weight, preferably from 10% by weight to 20% by weight, with respect to the total weight of the conjugated diene/solvent mixture.

Generally, said (co)polymerization can be carried out at a temperature ranging from −70° C. to +100° C., preferably from −20° C. to +80° C.

As far as the pressure is concerned, it is preferable to operate at the pressure of the components of the mixture to be (co)polymerized.

Said (co)polymerization can be carried out either in continuous or batchwise.

As indicated above, the use of the bis-imine pyridine complex of lanthanides having general formula (I) allows (co)polymers of conjugated dienes to be obtained, in particular linear or branched polybutadiene and polyisoprene, with a high content of 1,4-cis units, i.e. a content of 1,4-cis units 99% in the case of polybutadiene, and 98% in the case of polyisoprene. Some illustrative and non-limiting examples are provided hereunder for a better understanding of the present invention and for its practical embodiment.

EXAMPLES Reagents and Materials

The reagents and materials used in the following examples of the invention are indicated in the following list, together with their optional pretreatment and their supplier:

-   -   aniline (Aldrich): distilled before use;     -   neodymium trichloride/tetrahydrofuran complex [NdCl₃ (2THF)]:         obtained by the extraction of neodymium trichloride (NdCl₃)         (Strem Chemicals) with tetrahydrofuran (THF) at boiling point,         as described by Yang J. H. et al., in “Macromolecules” (1982),         Vol. 15(2), pages 230-233;     -   tetrahydrofuran (THF) (Carlo Erba, RPE): kept at reflux         temperature on potassium/benzophenone and then distilled under         nitrogen;     -   methanol (Carlo Erba, RPE): used as such;     -   ethanol (Carlo Erba, RPE): used as such;     -   isopropyl alcohol (Carlo Erba, RPE): used as such;     -   formic acid (85%) (Carlo Erba, RPE): used as such;     -   o-toluidine (Aldrich): used as such;     -   2-tert-butylaniline (Aldrich): used as such;     -   2,4,6-trimethylaniline (Aldrich): used as such;     -   2,6-di-isopropylaniline (Aldrich): used as such;     -   cyclohexylamine (Aldrich): used as such;     -   benzylamine (Aldrich): used as such;     -   2,6-diacetylpyridine (Aldrich): used as such;     -   glacial acetic acid (Aldrich): used as such;     -   toluene (Aldrich): pure, ≧99.5%, distilled on sodium (Na) in an         inert atmosphere;     -   1,3-butadiene (Air Liquide): pure, ≧99.5%, evaporated from the         container before each production, dried by passing it through a         column packed with molecular sieves and condensed inside the         reactor pre-cooled to −20° C.;     -   isoprene (Aldrich): pure, ≧99%, refluxed on calcium hydride,         then distilled “trap-to-trap” and kept in a nitrogen atmosphere;     -   tetra-iso-butyl-aluminoxane (TIBAO) (Akzo Nobel): cyclohexane         solution at 10% by weight;     -   methylaluminoxane (MAO) (Aldrich): toluene solution at 10% by         weight;     -   di-iso-butyl-aluminium hydride (DIBAH) (Aldrich): used as such;     -   Nd-2-ethylhexanoate [Nd(OCOC₁₇H₁₅)₃] (Aldrich): 0.05 M solution         in heptane;     -   heptane (Aldrich): pure, ≧99%, distilled on sodium (Na) in an         inert atmosphere;     -   pentane (Aldrich): pure, ≧99%, distilled on sodium (Na) in an         inert atmosphere;     -   di-ethyl aluminium chloride [AlEt₂Cl] (Akzo Nobel): used as         such;     -   tri-iso-butyl aluminium [TIBA] (Akzo Nobel): used as such;     -   deuterated tetrachloroethylene (C₂D₂Cl₄) (Acros): used as such;     -   deuterated chloroform deuterato (CDCl₃) (Acros): used as such.

The analysis and characterization methods indicated below were used.

Elemental Analysis

a) Determination of Nd

For the determination of the weight quantity of the metal Nd in the bis-imine pyridine complexes of lanthanides object of the present invention, an aliquot weighed exactly, operating in a dry-box under a nitrogen flow, of about 30-50 mg of sample, was placed in a platinum crucible of about 30 ml, together with a mixture of 1 ml of hydrofluoric acid (HF) at 40%, 0.25 ml of sulfuric (H₂SO₄) at 96% and 1 ml of nitric acid (HNO₃) at 70%. The crucible was then heated on a plate, increasing the temperature until the appearance of white sulfuric fumes (about 200° C.). The mixture thus obtained was cooled to room temperature (20° C.-25° C.), 1 ml of nitric acid (HNO₃) at 70% was added and the mixture was then heated until the appearance of fumes. After repeating the sequence a further two times, a limpid, almost colourless solution was obtained. 1 ml of nitric acid (HNO₃) and about 15 ml of water were then added, without heat, and the mixture was then heated to 80° C. for about 30 minutes. The sample thus prepared was diluted with water, having a MilliQ purity, up to a weight of about 50 g, weighed exactly, to obtain a solution on which analytical instrumental determination was carried out using an ICP-OES (optical detection plasma) Thermo Optek IRIS Advantage Duo spectrometer, by comparison with solutions at a known concentration. For this aim, a calibration curve was prepared for each analyte, within the range of 0 ppm-10 ppm, measuring solutions having a known titre obtained by weight dilution of certified solutions.

The solution of the sample prepared as described above was diluted again by weight so as to obtain concentrations close to those used as reference, before carrying out spectrophotometric detection. All the samples were prepared in duplicate. The results were considered acceptable if the single data of the tests in duplicate did not differ by more than 2% relative with respect to their average value.

b) Chlorine Determination

For this aim, samples of the bis-imine pyridine complexes of lanthanides object of the present invention, about 30 mg-50 mg, were weighed exactly in 100 ml glasses in a dry-box under a stream of nitrogen. 2 g of sodium carbonate (Na₂CO₃) and, outside the dry-box, ml of MillQ water, were added. The mixture was brought to boiling point, on a plate under magnetic stirring, for about 30 minutes. It was left to cool, sulfuric acid (H₂SO₄) diluted 1/5, was added until the reaction became acid and the mixture was titrated with silver nitrate (AgNO₃) 0.1N with a potentiometer titrimeter.

c) Determination of Carbon, Hydrogen and Nitrogen

The determination of the carbon, hydrogen and nitrogen, in the bis-imine pyridine complexes of lanthanides object of the present invention, and also in the ligands used for the aim of the present invention, was carried out by means of an automatic analyzer Carlo Erba Mod. 1106.

¹³C-HMR and ¹H-HMR Spectra

The ¹³C-HMR and ¹H-HMR spectra were registered by means of a nuclear magnetic resonance spectrometer mod. Bruker Avance 400, using deuterated tetrachloroethylene (C₂D₂Cl₄) at 103° C., and hexamethyldisiloxane (HDMS) as internal standard, or using deuterated chloroform (CDCl₃), at 25° C., and tetramethylsilane (TMS) as internal standard. Solutions of the ligands used in the present invention or polymeric solutions having concentrations equal to 10% by weight with respect to the total weight of the solution of ligands used in the present invention or polymeric solution, respectively, were used for the aim.

The microstructure of the polymers [i.e. content of 1,4-cis units (%)] was determined by analysis of the above spectra on the basis of what is indicated in literature by Mochel, V. D., in “Journal of Polymer Science Part A-1: Polymer Chemistry” (1972), Vol. 10, Issue 4, pages 1009-1018, for polybutadiene; and by Sato, H., et al., in “Journal of Polymer Science: Polymer Chemistry Edition” (1979), Vol. 17, Issue 11, pages 3551-3558 for polyisoprene.

I.R. Spectra

The I.R. spectra (FT-IR) were registered by means of a Bruker IFS 48 spectrophotometer.

The I.R. spectra (FT-IR) of the ligands used in the present invention were obtained by dispersing the ligand to be analyzed in anhydrous potassium bromide (KBr) (disks of KBr), or in a suspension of nujol.

The I.R. spectra (FT-IR) of the bis-imine pyridine complexes of lanthanides object of the present invention, were obtained by dispersing the bis-imine pyridine complex of lanthanides to be analyzed in anhydrous potassium bromide (KBr) (disks of KBr), or in a suspension of nujol.

The I.R. spectra (FT-IR) of the polymers were obtamed from polymeric films on tablets of potassium bromide (KBr), said films being obtained by deposition of a solution of the polymer to be analyzed in hot odichlorobenzene. The concentration of the polymeric solutions analyzed was equal to 10% by weight with respect to the total weight of the polymeric solution.

Thermal Analysis (DSC)

The DSC (“Differential Scanning calorimetry”) thermal analysis, for determining the melting point (T_(m)) and the crystallization temperature (T_(c)) of the polymers obtamed, was carried out using a Perkin Elmer Pyris differential scanning calorimeter. For this aim, 5 mg of polymer were analyzed, with a scanning rate ranging from 1° C./min to 20° C./min, in an inert nitrogen atmosphere.

The DSC (“Differential Scanning calorimetry”) thermal analysis, for determining the glass transition temperature (TO of the polymers obtained and of the natural rubber (NR), was carried out by means of the above calorimeter, using the following thermal program: isotherm for 3 minutes at +70° C.; cooling from +70° C. to −90° C. at a rate of 10° C./min; isotherm for 3 min at −90° C.; heating from −90° C. to +70° C. at a rate of 10° C./min.

Molecular Weight Determination

The determination of the molecular weight (MW) of the polymers obtained was carried out by means of GPC (“Gel Permeation Chromatography”) operating under the following conditions:

-   -   Agilent 1100 pump;     -   I.R. Agilent 1100 detector;     -   PL Mixed-A columns;     -   solvent/eluent: tetrahydrofuran (THF);     -   flow-rate: 1 ml/min;     -   temperature: 25° C.;     -   molecular mass calculation: Universal Calibration method.

The weight average molecular weight (M_(w)) and the polydispersity Index (PDI) corresponding to the M_(w)/M_(n) ratio (M_(n)=number average molecular weight), are specified.

Determination of the Branching

The determination of the branching of the polymers obtained was carried out by means of the GPC/MALLS technique obtained by coupling a multi-angle light scattering detector (MALLS) with a traditional SEC/RI elution system, operating under the following conditions:

Agilent 1050 pump;

I.R. Agilent 1050 detector;

MALLS Dawn-DSP Wyatt detector—Technology, λ=632.8 nm;

PL GEL Mixed-A (×4) columns;

solvent/eluent: tetrahydrofuran (THF);

flow-rate: 1 ml/min;

temperature: 25° C.

Operating as described above, the absolute measurement can be contemporaneously carried out of the molecular weight and of the gyration radius of the macromolecules that are separated by the chromatographic system: the quantity of light scattered from a macromolecular species in solution can in fact be used directly for obtaining its molecular weight, whereas the angular variation in the scattering is directly correlated to its average dimensions. The fundamental relation which is used is represented by the following equation (1):

$\begin{matrix} {\frac{K*c}{R_{\theta}} = {\frac{1}{M_{w}P_{\theta}} + {2A_{2}c}}} & (1) \end{matrix}$

wherein: K* is the optical constant which depends on the wavelength of the light used, the refraction index (dn/dc) of the polymer, the solvent used; M_(w) is the weight average molecular weight; c is the concentration of the polymeric solution; R_(θ) is the intensity of the light scattered, measured at the angle θ (excess Rayleigh factor);

P_(θ) is the function describing the variation of the light scattered with the angle at which it is measured, for an angle θ equal to 0;

A₂ is the second virial coefficient.

For very low concentrations (typical of a GPC system), the equation (1) indicated above is reduced to the following equation (2):

$\begin{matrix} {\frac{K*c}{R_{\theta}} = \frac{1}{M_{w}P_{\theta}}} & (2) \end{matrix}$

wherein K*, c, R_(θ), M_(w) and P_(θ), have the same meanings defined above, and by carrying out the measurement on several angles, the extrapolation to angle null of the function K*c/R_(θ) in relation to sen²θ/2 directly provides the molecular weight from the intercept value and the gyration radius of the slope.

Furthermore, as this measurement is carried out for every slice of the chromatogram, it is possible to obtain a distribution of both the molecular weight and the gyration radius.

The macromolecular dimensions in solution are directly correlated to their branching degree: for the same molecular weight, the smaller the dimensions of the macromolecule with respect to the linear correspondent, the higher the branching degree will be.

Informations relating to the macrostructure of the polymer is qualitatively deduced from the value of the parameter α, which represents the slope of the curve which correlates the gyration radius with the molecular weight: when, under the same analysis conditions, this value decreases with respect to a macrostructure of the linear type, there is the presence of a polymer having a branched-type macrostructure. The typical value of the parameter α, for linear polybutadiene having a high content of 1,4-cis units, in tetrahydrofuran (THF), is equal to 0.58-0.60.

Example 1 Synthesis of the Ligand Having Formula (L1)

2.10 ml (0.023 moles) of aniline were introduced into a reaction flask together with 5 ml of methanol and 5 drops of formic acid, obtaining a solution. 20 ml of methanol containing 1.79 g (0.011 moles) of diacetylpyridine, were subsequently added, dropwise, at room temperature, to said solution. The solution was left under stirring the whole night obtaining the precipitation of a yellow microcrystalline solid: said yellow solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 2.76 g of a yellow solid (yield=80%) having formula (L1).

Elemental analysis [found (calculated)]: C, 80.9% (80.5%); H, 6.13% (6.11%); N, 13.6% (13.4%).

Molecular weight (MW): 313.4.

FT-IR (nujol): 1632 cm⁻¹ ν_((C═N)).

¹H-NMR (CDCl₃): 2.4 (s, 6H), 6.84 (d, 4H), 7.11 (t, 2H), 7.36 (t, 4H), 7.88 (t, 1H), 8.36 (d, 2H).

Example 2 Synthesis of the Ligand Having Formula (L2)

2.44 ml (0.023) of o-toluidine were introduced into a reaction flask together with 5 ml of methanol and 5 drops of formic acid, obtaining a solution. 20 ml of methanol containing 1.79 g (0.011 moles) of 2,6-diacetylpyridine were subsequently added, dropwise, at room temperature, to said solution. The solution was left under stirring the whole night obtaining the precipitation of a yellow microcrystalline solid: said yellow solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 1.52 g of a yellow solid (yield=40%) having formula (L2).

Elemental analysis [found (calculated)]: C, 81.2% (80.9%); H, 6.83% (6.76%); N, 12.2% (12.3%).

Molecular weight (MW): 341.46.

FT-IR (nujol): 1641 cm⁻¹ ν_((C═N)).

¹H-NMR (CDCl₃): 2.4 (s, 6H), 6.84 (d, 4H), 7.11 (t, 2H), 7.28 (t, 4H), 7.91 (t, 1H), 8.49 (d, 2H).

Example 3 Synthesis of the Ligand Having Formula (L3)

A solution of 2,6-diisopropylaniline (3.47 ml; 0.0184 moles) in methanol (10 ml) was added, dropwise, to a solution of 2,6-diacetylpyridine (1.5 g; 0.0092 moles) in methanol (25 ml) and 5 drops of formic acid were subsequently added, obtaining a solution. Said solution was subsequently heated to reflux temperature, for 48 hours. At the end, the solution was concentrated to half of its volume and cooled in a freezer, obtaining the precipitation of a yellow microcrystalline solid: said yellow solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 3.5 g of a yellow solid (yield=80%) having formula (L3).

Elemental analysis [found (calculated)]: C, 81.9% (82.28%); H, 8.5% (9%); N, 8.72% (8.72%).

Molecular weight (MW): 481.72.

FT-IR (nujol): 1646 cm⁻¹ ν_((C═N)).

¹H-NMR (CDCl₃): 1.15 (d, 24H), 2.24 (s, 6H), 2.81 (m, 4H), 7.15 (m, 6H), 7.9-8.5 (m, 3H).

Example 4 Synthesis of the Ligand Having Formula (L4)

1.944 g (0.0196 moles) of cyclohexylamine were poured into a reaction flask together with 10 ml of ethanol and 3 drops of formic acid, obtaining a solution. 20 ml of ethanol containing 1.6 g (0.0098 moles) of 2,6-diacetylpyridine, were subsequently added, dropwise, at room temperature, to said solution, The solution was left under stirring the whole night obtaining the precipitation of a whitish microcrystalline solid: said whitish solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 1.5 g of a whitish solid (yield=47%) having formula (L4).

Elemental analysis [found (calculated)]: C, 76.68% (77.49%); H, 9.42% (9.60%); N, 12.49% (12.91%).

Molecular weight (MW): 325.50.

FT-IR (nujol): 1635 cm⁻¹ ν_((C═N)).

¹H-NMR (CDCl₃): 2.4 (s, 6H), 6.84 (d, 4H), 7.11 (t, 2H), 7.28 (t, 4H), 7.91 (t, 1H), 8.49 (d, 2H).

Example 5 Synthesis of the Ligand Having Formula (L5)

2.13 ml (0.012 moles) of 2,6-diisopropylaniline were introduced into a reaction flask together with 5 ml of methanol and 3 drops of formic acid, obtaining a solution. 20 ml of methanol containing 1.93 g (0.012 moles) of 2,6-diacetylpyridine were subsequently added dropwise, at room temperature, to said solution, obtaining the precipitation of a yellow microcrystalline solid: after 1 hour, said yellow solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 2.53 g of a light-yellow solid (yield=65%) having formula (L5a):

Elemental analysis [found (calculated)]: C, 77.8% (78.2%); H, 8.29% (8.13%); N, 8.51% (8.69%).

Molecular weight (MW): 322.45.

FT-IR (nujol): 1699 cm⁻¹ ν_((C═O)), 1645 cm⁻¹ ν_((C═N))

¹H-NMR (CDCl₃): 1.16 (d, 6H), 1.17 (d, 6H), 2.28 (s, 3H), 2.74 (m, 2H), 2.81 (s, 3H), 7.08-7.22 (m, 3H), 7.95 (t, 1H), 8.16 (dd, 1H), 8.58 (dd, 1H).

2.0 g (6.2×10⁻³ moles) of the compound having formula (L5a) obtained as described above, were dissolved in 100 ml of warm isopropyl alcohol and, subsequently, 5 drops of formic acid and, dropwise, 0.62 g (6.82×10⁻³ moles) of freshly distilled aniline, were added: the whole mixture was left at reflux, for 8 hours, obtaining 1.5 g of a yellow solid (yield=61%) having formula (L5).

Elemental analysis [found (calculated)]: C, 81.10% (81.57%); H, 7.93% (7.86%); N, 10.40% (10.57%).

Molecular weight (MW): 397.56.

FT-IR (nujol): 1637 cm⁻¹ ν_((C═O)), 1639 cm⁻¹ ν_((C═N)).

FIG. 11 shows the FT-IR (nujol) spectrum of the ligand having formula (L5) obtained.

Example 6 Synthesis of the Ligand Having Formula (L6)

5.37 g (0.036 moles) of 2-tert-butylaniline were introduced into a reaction flask together with 15 ml of methanol and 5 drops of formic acid, obtaining a solution. 30 ml of methanol containing 5.87 g (0.036 moles) of 2,6-diacetylpyridine were subsequently added dropwise, at room temperature, to said solution, obtaining the precipitation of a yellow microcrystalline solid: after 1 hour, said yellow solid was recovered by filtration, washed with cold methanol and dried, under vacuum, at room temperature, obtaining 9.84 g of a light-yellow solid (yield=93%) having formula (L6a):

Elemental analysis [found (calculated)]: C, 78.0% (77.5%); H, 7.60% (7.53%); N, 9.65% (9.52%).

Molecular weight (MW): 294.4.

FT-IR (nujol): 1694 cm⁻¹ ν_((C═O)), 1644 cm⁻¹ ν_((C═N))

¹H-NMR (CDCl₃): 1.39 (s, 9H), 2.41 (s, 3H), 2.80 (s, 3H), 2.54 (dd, 1H), 7.24 (m, 2H), 7.43 (dd, 1H), 7.95 (t, 1H), 8.13 (dd, 1H), 8.50 (dd, 1H).

6.90 g (2.35×10⁻² moles) of the compound having formula (L6a) obtained as described above, were refluxed in 100 ml of absolute ethanol, and 2.19 g (2.35×10⁻² moles) of freshly distilled aniline were then added dropwise: the whole mixture was left at reflux, for 8 hours, obtaining 6.3 g of a yellow solid (yield=73%) having formula (L6).

Elemental analysis [found (calculated)]: C, 81.20% (81.26%); H, 7.30% (7.37%); N, 11.47% (11.37%).

Molecular weight (MW): 369.50.

FT-IR (nujol): 1636 cm⁻¹ ν_((C═N)).

Example 7 Synthesis of the Ligand (L7)

2.0 g (6.2×10⁻³ moles) of the compound (L5a) obtained as described above, were introduced into a reaction flask with 100 ml of absolute ethanol, and 0.75 g (6.82×10⁻³ moles) of benzylamine and 5 drops of glacial acetic acid were then added, under stirring: the whole mixture was left, under stirring, at room temperature, for 24 hours, obtaining 5.74 g of a light-yellow solid (yield=65%) having formula (L7).

Elemental analysis [found (calculated)]: C, 81.2% (81.71%); H, 8.1% (8.08%); N, 9.7% (10.21%).

Molecular weight (MW): 411.59.

FT-IR (nujol): 1634 cm⁻¹ ν_((C═N)).

Example 8 Synthesis of the Ligand Having Formula (L8)

6.90 g (2.35×10⁻² moles) of the compound (L6a) obtained as described above, were refluxed in 100 ml of absolute ethanol, and 2.30 g (2.35×10⁻² moles) of cyclohexylamine were then added dropwise: the whole mixture was left at reflux temperature, for 8 hours, obtaining 5.74 g of a yellow solid (yield=65%) having formula (L8).

Elemental analysis [found (calculated)]: C, 80.05% (79.95%); H, 8.90% (8.86%); N, 11.20% (11.19%).

Molecular weight (MW): 375.55.

FT-IR (nujol): 1637 cm⁻¹ ν_((C═N)).

Example 9 Synthesis of NdCl₃(L1) [Sample GL380/P1891]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] (0.641 g; 1.6×10⁻³ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (50 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L1) (0.564 g; 1.8×10⁻³ moles; molar ratio L1/Nd=1.13), obtained as described in Example 1, was then added. The whole mixture was kept under stirring, at room temperature, for 72 hours, obtaining an extremely dense white/green suspension. At the end of the reaction, the solvent was almost completely removed by volume under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a white/green solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The white/green residue remaining on the filter was recovered and dried under vacuum obtaining 0.780 g of a solid product corresponding to the complex NdCl₃(L1), equal to a conversion of 86.4% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 44.60% (44.72%); H, 3.30% (3.40%); N, 7.30% (7.45%); Cl, 19.0% (18.86%); Nd, 25.60% (25.57%).

Molecular weight (MW): 564.0.

FT-IR (nujol): 1645 cm⁻¹ ν_((C═N)).

Example 10 Synthesis of NdCl₃(L2) [Sample GL360]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] (0.305 g; 7.72×10⁻⁴ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (35 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L2) (0.313 g; 9×10⁻⁴ moles; molar ratio L2/Nd=1.2), obtained as described in Example 2, was then added. The whole mixture was kept under stirring, at room temperature, for 2 days: at the beginning a green/yellow suspension was formed which subsequently became red-coloured as the reaction proceeded. At the end of the reaction, the solvent was considerably reduced in volume under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a red solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The red-coloured residue remaining on the filter was recovered and dried under vacuum obtaining 0.425 g of a solid product corresponding to the complex NdCl₃(L2), equal to a conversion of 93% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 46.50% (46.66%); H, 3.80% (3.92%); N, 6.90% (7.10%); Cl, 18.10% (17.96%); Nd, 24.50% (24.36%).

Molecular weight (MW): 592.05.

FT-IR (nujol): 1648 cm⁻¹ ν_((C═N)).

Example 11 Synthesis of NdCl₃(L4) [Sample P1888]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] ((0.7 g; 1.8×10⁻³ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (50 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L4) (0.762 g; 2.3×10⁻³ moles; molar ratio L4/Nd=1.3), obtained as described in Example 3, was then added. The whole mixture was kept under stirring, at room temperature, for 3 days: at the beginning a yellowish suspension was formed which subsequently became yellow/red-coloured as the reaction proceeded. At the end of the reaction, the solvent was considerably reduced in volume under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a yellowish solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The yellowish residue remaining on the filter was recovered and dried under vacuum obtaining 0.860 g of a solid product corresponding to the complex NdCl₃(L4), equal to a conversion of 82.9% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 43.60% (43.78%); H, 5.30% (5.42%); N, 7.20% (7.29%); Cl, 18.5% (18.46); Nd, 25.10% (25.04%).

Molecular weight (MW): 576.0.

FT-IR (nujol): 1589 cm⁻¹ ν_((C═N)).

Example 12 Synthesis of NdCl₃(L5) [Sample P1963]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] (0.557 g; 1.4×10⁻³ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (50 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L5) (0.729 g; 1.83×10⁻³ moles; molar ratio L5/Nd=1.3), obtained as described in Example 5, was then added. The whole mixture was kept under vigorous stirring, at room temperature, for days obtaining a relatively homogeneous greencoloured solution. At the end of the reaction, the solvent was partially removed under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a greenish solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The greenish residue remaining on the filter was recovered and dried under vacuum obtaining 0.798 g of a solid product corresponding to the complex NdCl₃(L5), equal to a conversion of 87.9% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 50.10% (50.03%); H, 4.90% (4.82%); N, 6.60% (6.48%); Cl, 16.5% (16.41); Nd, 22.30% (22.25%).

Molecular weight (MW): 648.16.

FT-IR (nujol): 1643 cm⁻¹ (ν_(C═N—Nd)); 1605 cm⁻¹ (ν_((Py)NNd)).

FIG. 12 shows the FT-IR spectrum of the complex NdCl₃(L5).

Example 13 Synthesis of NdCl₃(L6) [Sample P1965]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] (0.497 g; 1.26×10⁻³ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (40 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L6) (0.605 g; 1.64×10⁻³ moles; molar ratio L6/Nd=1.3), obtained as described in Example 6, was then added. The whole mixture was kept under stirring, at room temperature, for 4 days obtaining a relatively homogeneous greenish solution. At the end of the reaction, the solvent was partially removed under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a greenish solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The greenish residue remaining on the filter was recovered and dried under vacuum obtaining 0.692 g of a solid product corresponding to the complex NdCl₃(L6), equal to a conversion of 88.5% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 48.20% (48.42%); H, 4.30% (4.39%); N, 6.60% (6.78%); Cl, 17.2% (17.15%); Nd, 23.30% (23.26%).

Molecular weight (MW): 620.10.

FT-IR (nujol): 1645 cm⁻¹ (ν_(C═N—Nd)); 1605 cm⁻¹ (ν_((Py)NNd)).

Example 14 Synthesis of NdCl₃(L8) [Sample P1964]

The complex neodymium trichloride/tetrahydrofuran [NdCl₃(2THF)] (0.522 g; 1.32×10⁻³ moles) was introduced into a 100 ml reaction flask together with tetrahydrofuran (THF) (40 ml). The whole mixture was kept under stirring, at room temperature, for a few minutes, and the ligand having formula (L8) (0.645 g; 1.72×10⁻³ moles; molar ratio L8/Nd=1.3), obtained as described in Example 8, was then added. The whole mixture was kept under stirring, at room temperature, for 4 days obtaining a relatively homogeneous greenish solution. At the end of the reaction, the solvent was partially removed under vacuum, pentane in excess was added and the whole mixture was subsequently filtered obtaining a greenish solid residue which was washed various times with pentane, in order to remove the non-reacted ligand. The greenish residue remaining on the filter was recovered and dried under vacuum obtaining 0.645 g of a solid product corresponding to the complex NdCl₃(L8), equal to a conversion of 78% with respect to the neodymium charged.

Elemental analysis [found (calculated)]: C, 48.10% (47.96%); H, 5.40% (5.31%); N, 6.90% (6.71%); Cl, 19.5% (19.59%); Nd, 26.50% (26.56%).

Molecular weight (MW): 626.15.

FT-IR (nujol): 1643 cm⁻¹ (ν_(C═N—Nd)); 1604 cm⁻¹ (ν_((Py)NNd)).

Example 15 P1920

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 7 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 9. The whole mixture was kept, under magnetic stirring, at 20° C., for 3 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.603 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 16 P1941

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.9 ml of toluene were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 9. The whole mixture was kept, under magnetic stirring, at 20° C., for 116 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.755 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 17 A007

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 13.02 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 9. The whole mixture was kept, under magnetic stirring, at 20° C., for 8 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.443 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 18 GL503

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.85 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L2) [sample GL360] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.9 mg) obtained as described in Example 10. The whole mixture was kept, under magnetic stirring, at 20° C., for 8 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.603 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 2( b) shows the FT-IR spectrum of the polybutadiene obtained.

Example 19 GL416

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.75 ml of toluene were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L2) [sample GL360] (2.95 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻² moles, equal to about 5.9 mg) obtained as described in Example 10. The whole mixture was kept, under magnetic stirring, at 20° C., for 720 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.867 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 20 A008

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 12.87 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L2) [sample GL360] (2.95 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 10. The whole mixture was kept, under magnetic stirring, at 20° C., for 4 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.603 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 21 GL596

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.9 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 20° C., for 3 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.668 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtamed are indicated in Table 1.

Example 22 P1942

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.8 ml of toluene were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 20° C., for 20 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.917 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 23 P1962

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 12.92 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 20° C., for 30 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.637 g of polybutadiene having a content of 1,4-cis units equal to 99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 3 shows the ¹H-NMR and ¹³C-NMR spectra of the polybutadiene obtained.

Example 24 GL734

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.7 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L6) [sample P1965] (3.1 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.2 mg) obtained as described in Example 13. The whole mixture was kept, under magnetic stirring, at 20° C., for 12 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.102 g of polybutadiene having a content of 1,4-cis units equal to 99.7%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 5 shows the ¹H-NMR and ¹³C-NMR spectra of the polybutadiene obtained.

Example 25 A001

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.8 ml of toluene were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L6) [sample P1965] (3.1 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.2 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 20° C., for 110 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.588 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 26 A002

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 12.72 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L6) [sample P1965] (3.1 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.2 mg) obtained as described in Example 13. The whole mixture was kept, under magnetic stirring, at 20° C., for 24 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.605 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 27 GL732

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.55 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L5) [sample P1963] (3.25 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.5 mg) obtained as described in Example 12. The whole mixture was kept, under magnetic stirring, at 20° C., for 29 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.462 g of polybutadiene having a content of 1,4-cis units equal to 99.9%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 2 (c) shows the FT-IR spectrum of the polybutadiene obtained.

FIG. 6 shows the ¹H-NMR and ¹³C-NMR spectra of the polybutadiene obtained.

Example 28 A003

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.45 ml of toluene were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L5) [sample P1963] (3.25 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.5 mg) obtained as described in Example 12. The whole mixture was kept, under magnetic stirring, at 20° C., for 116 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.287 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 29 A004

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 12.57 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L5) [sample P1963] (3.25 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.5 mg) obtained as described in Example 12. The whole mixture was kept, under magnetic stirring, at 20° C., for 60 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.435 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 30 GL733

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.65 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Tetra-iso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.2 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L8) [sample P1964] (3.15 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.3 mg) obtained as described in Example 14. The whole mixture was kept, under magnetic stirring, at 20° C., for 29 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.280 g of polybutadiene having a content of 1,4-cis units equal to 99.6%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 2 (d) shows the FT-IR spectrum of the polybutadiene obtained.

FIG. 4 shows the ¹H-NMR and ¹³C-NMR spectra of the polybutadiene obtained.

Example 31 A005

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 6.55 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Methylaluminoxane (MAO) in a toluene solution (6.3 ml; 1×10⁻² moles, equal to about 0.58 g) was then added, and subsequently the complex NdCl₃(L8) [sample P1964] (3.15 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.3 mg) obtained as described in Example 14. The whole mixture was kept, under magnetic stirring, at 20° C., for 116 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.312 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 32 A006

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 12.67 ml of heptane were then added and the temperature of the solution thus obtained was brought to 20° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L8) [sample P1964] (3.15 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 6.3 mg) obtained as described in Example 14. The whole mixture was kept, under magnetic stirring, at 20° C., for 60 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.420 g of polybutadiene having a content of 1,4-cis units >99%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

Example 33 Preparation of the Preformed Ternary Catalytic System AlEt₂Cl/Nd (OCOC₂H₁₅)₂/Al (^(i)Bu)₃

15 ml of a heptane solution 0.05 M of neodymium 2-ethylhexanoate [Nd(OCOC₂H₁₅)₃] (7.5×10⁻⁴ moles), 16.6 ml of heptane and 0.29 ml of di-ethyl aluminium chloride (AlEt₂Cl) (2.3×10⁻³ moles) were introduced, consecutively, into a 50 ml test-tube. Upon the addition of di-ethyl aluminium chloride (AlEt₂Cl), a whitish suspension was immediately formed, which was kept, under stirring, at room temperature, for 15 minutes. Tri-isobutylaluminium [Al(^(i)Bu)₂] (5.63 ml; 2.25×10⁻² moles) was subsequently added and the solution obtained was left to age for 2 hours, under constant stirring, at 20° C., obtaining a catalytic suspension having a concentration of neodymium equal to 0.02 M.

Example 34 Comparative

2 ml of 1,3-butadiene, equal to about 1.4 g, were condensed, at a low temperature (−20° C.), in a 25 ml test-tube. 7 ml of heptane were then added and the temperature of the solution was maintained at 20° C. The preformed ternary catalyst AlEt₂Cl/Nd(OCOC₂H₁₅)₂/A(^(i)Bu)₂ (0.5 ml; 1×10⁻⁵ moles of Nd), obtained as described in Example 33, was then added. The whole mixture was kept, under magnetic stirring, at 20° C., for 1.25 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.780 g of polybutadiene having a content of 1,4-cis units equal to about 96%: further characteristics of the process and of the polybutadiene obtained are indicated in Table 1.

FIG. 1 shows the ¹H-NMR spectrum of the polybutadiene obtained.

FIG. 2 (a) shows the FT-IR spectrum of the polybutadiene obtained.

TABLE 1 Polymerization of 1,3-butadiene with catalytic systems prepared in situ Al/Ln M. (molar Conversion N^((a)) P.^((b)) T_(c) ^((c)) M_(w) × 10⁻³ Ex. ratio) (%) (h⁻¹) (° C.) (° C.) (g × mol⁻¹) M_(w)/M_(n) α^((d)) 15 1000 43.1 279 −2.2 −22.2 877 8.6 0.61 16 1000 53.9 12 −3.1 −24.2 440 5.1 0.55 17 100 30.7 99 −1.9 −21.8 680 9.5 0.63 18 1000 87.1 141 −1.5 −20.4 348 11.4 0.62 19 1000 61.9 2 −2.8 −23.9 276 6.6 0.56 20 100 34.8 45 −2.1 −21.9 650 4.9 0.60 21 1000 47.7 165 −1.6 −20.7 780 7.2 0.61 22 1000 65.5 14 −2.7 −22.9 620 8.9 0.55 23 100 45.5 39 −3.7 −28.5 650 5.8 0.62 24 1000 78.7 170 −1.3 −20.2 760 6.5 0.63 25 1000 42 9 −2.1 −21.7 220 2.8 0.57 26 100 43.2 47 −1.6 −20.7 580 5.1 0.59 27 1000 33 30 −1.1 −19.9 690 7.1 0.60 28 1000 20.5 5 −1.9 −22 195 3.5 0.56 29 100 31.1 13 −1.5 −20.5 570 5.2 0.62 30 1000 20 18 −1.4 −20.4 720 6 0.61 31 1000 22.3 5 −2.0 −222.1 320 3.7 0.56 32 100 30 13 −1.8 −21.5 560 4.8 0.62 34^((e)) 33 50 515 −6 −33 550 5 0.60 ^((a))number of moles of 1,3-butadiene polymerized per hour per mole of lanthanide; ^((b))melting point; ^((c))crystallization temperature; ^((d))linearity index of polybutadiene; ^((e))polymerization carried out with the preformed catalyst prepared as described in Example 33.

Example 35 GL760

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 7 ml of heptane were then added and the temperature of the solution was maintained at 20° C. Tetra-isobutyl-aluminoxane (TIBAO) in a cyclohexane solution (6.22 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 9. The whole mixture was kept, under magnetic stirring, at 20° C., for 45 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.129 g of polyisoprene having a content of 1,4-cis units equal to 98%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

FIG. 7 shows the ¹H-NMR and ¹³C-NMR spectra of the polyisoprene obtained.

Example 36 GL800

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 7 ml of heptane were then added and the temperature of the solution was brought to 50° C. Tetra-isobutyl-aluminoxane (TIBAO) in a cyclohexane solution (6.22 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtained as described in Example 9. The whole mixture was kept, under magnetic stirring, at 50° C., for 23 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.36 g of polyisoprene having a content of 1,4-cis units >98% and a glass transition temperature (T_(g)) equal to −66.0° C.: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

FIG. 8 shows the DSC diagram of the polyisoprene obtained.

Example 37 GL805

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 13.2 ml of heptane were then added and the temperature of the solution thus obtained was brought to 50° C. Di-iso-butyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L1) [sample GL380/P1891] (2.8 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.6 mg) obtamed as described in Example 9. The whole mixture was kept, under magnetic stirring, at 50° C., for 24 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.36 g of polyisoprene having a content of 1,4-cis units >98%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

Example 38 P1885

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 6.83 ml of heptane were then added and the temperature of the solution was maintained at 20° C. Tetraiso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.22 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L2) [sample GL360] (2.95 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.9 mg) obtained as described in Example 10. The whole mixture was kept, under magnetic stirring, at 20° C., for 48 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.447 g of polyisoprene having a content of 1,4-cis units >98%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

Example 39 GL759

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 6.9 ml of heptane were then added and the temperature of the solution was maintained at 20° C. Tetraiso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.22 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 20° C., for 45 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.307 g of polyisoprene having a content of 1,4-cis units >98%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

Example 40 GL799

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 6.9 ml of heptane were then added and the temperature of the solution was brought to 50° C. Tetraiso-butyl-aluminoxane (TIBAO) in a cyclohexane solution (6.22 ml; 1×10⁻² moles, equal to about 2.9 g) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 50° C., for 22.5 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.36 g of polyisoprene having a content of 1,4-cis units >98% and a glass transition temperature (T_(g)) equal to −66.3° C.: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

FIG. 9 shows the DSC diagram of the polyisoprene obtained.

Example 41 GL802

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 12.92 ml of heptane were then added and the temperature of the solution was brought to 50° C. Di-isobutyl-aluminium hydride (DIBAH) (0.18 ml; 1 mmole, equal to about 144 mg) was then added, and subsequently the complex NdCl₃(L4) [sample P1888] (2.9 ml of a toluene solution at a concentration equal to 2 mg/ml; 1×10⁻⁵ moles, equal to about 5.8 mg) obtained as described in Example 11. The whole mixture was kept, under magnetic stirring, at 50° C., for 24 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 1.36 g of polyisoprene having a content of 1,4-cis units >98%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

Example 42 Comparative

2 ml of isoprene, equal to about 1.36 g, were introduced, at a temperature of 20° C., into a 25 ml test-tube. 7 ml of heptane were then added and the temperature of the solution was maintained at 20° C. The preformed ternary catalyst AlEt₂Cl/Nd (OCOC₇H₁₅)₃/Al (^(i)BU)₃ (0.5 ml; 1×10⁻⁵ moles of Nd), obtained as described in Example 33, was then added. The whole mixture was kept, under magnetic stirring, at 20° C., for 6 hours. The polymerization was then quenched by the addition of 2 ml of methanol containing a few drops of hydrochloric acid. The polymer obtained was subsequently coagulated by the addition of 40 ml of a methanol solution containing 4% of antioxidant Irganox® 1076 (Ciba) obtaining 0.544 g of polyisoprene having a content of 1,4-cis units equal to about 94%: further characteristics of the process and of the polyisoprene obtained are indicated in Table 2.

FIG. 1 shows the ¹H-NMR spectrum of the polyisoprene obtained.

TABLE 2 Polymerization of isoprene with catalytic systems prepared in situ Al/Ln (molar Conversion N^((a)) M_(w) × 10⁻³ T_(g) ^((b)) Example ratio) (%) (h⁻¹) (g × mol⁻¹) M_(w)/M_(n) (° C.) 35 1000 83 37 814 4.5 −66.4 36 1000 100 87 680 4.8 −66.0 37 100 100 83 600 6.2 −66.0 38 1000 32.9 14 902 6 −65.5 39 1000 22.6 10 945 5.3 −65.8 40 1000 100 89 820 4.9 −66.3 41 100 100 83 790 5.5 −65.7 42 33 40 133 400 4 −62.1 NR^((c)) — — — — — −66.2 ^((a))number of moles of isoprene polymerized per hour per mole of lanthanide; ^((b))glass transition temperature; ^((c))natural rubber (FIG. 10 shows the DSC diagram of natural rubber). 

1. A bis-imine pyridine complex of lanthanides having general formula (I):

wherein: Ln represents a metal of the series of lanthanides; R₁ and R₂, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups, cycloalkyl groups optionally substituted, aryl groups optionally substituted; R₃ and R₄, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups, cycloalkyl groups optionally substituted, aryl groups optionally substituted; or R₂ and R₄ can be optionally bound to each other so as to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic cycle containing from 3 to 6 carbon atoms, optionally substituted with linear or branched C₁-C₂₀ alkyl groups, said cycle optionally containing other heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; or R₁ and R₃ can be optionally bound to each other so as to form, together with the other atoms to which they are bound, a saturated, unsaturated or aromatic cycle containing from 3 to 6 carbon atoms, optionally substituted with linear or branched C₁-C₂₀ alkyl groups, said cycle optionally containing other heteroatoms; and X₁, X₂ and X₃, equal to or different from each other, represent a halogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups, —OCOR₅ or —OR₅ groups wherein R₅ is selected from linear or branched C₁-C₂₀ alkyl groups.
 2. The bis-imine pyridine complex of lanthanides having general formula (I) according to claim 1, wherein Ln represents neodymium (Nd), lanthanum (La), praseodymium (Pr), gadolinium (Gd), europium (Eu), terbium (Tb), samarium (Sm), erbium (Er), or ytterbium (Yb).
 3. The bis-imine pyridine complex of lanthanides having general formula (I) according to claim 1, wherein: Ln is neodymium (Nd), praseodymium (Pr), gadolinium (Gd), or lanthanum (La); R₁ and R₂, the same as each other, are a hydrogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups; or they are selected from cycloalkyl groups optionally substituted; R₃ and R₄, equal to or different from each other, are selected from phenyl groups, optionally substituted; or they are selected from cycloalkyl groups optionally substituted; X₁, X₂ and X₃, the same as each other, are a halogen atom.
 4. A catalytic system for the (co)polymerization of conjugated dienes comprising: (a) at least one bis-imine pyridine complex of lanthanides having general formula (I) according to claim 1; (b) at least one co-catalyst selected from: (b1) aluminium alkyls having general formula (II): Al(X′)_(n)(R₆)_(3-n)  (II) wherein X′ represents a halogen atom; R₆ is selected from linear or branched C₁-C₂₀ alkyl groups, C₃-C₂₀ cycloalkyl groups, aryl groups, said groups being optionally substituted with one or more atoms of silicon or germanium; and n is an integer ranging from 0 to 2; (b2) aluminium oxanes having general formula (III): (R₇)₂—Al—O—[—Al(R₈)—O—]_(p)—Al—(R₉)₂  (III) wherein R₇, R₈ and R₉, equal to or different from each other, represent a hydrogen atom, a halogen atom; or they are selected from linear or branched C₁-C₂₀ alkyl groups, C₃-C₂₀ cycloalkyl groups, aryl groups, said groups being optionally substituted with one or more atoms of silicon or germanium; and p is an integer ranging from 0 to 1,000; and (b3) compounds having general formula (IV): D⁺E⁻  (IV) wherein D⁺ represents a Brønsted acid capable of releasing a proton and of reacting irreversibly with the substituent X of the bis-imine pyridine complex of lanthanides having general formula (I); E⁻ represents a compatible anion capable of stabilizing the active catalytic species generated by the reaction of the two components and which is sufficiently labile as to be removed by an olefin monomer, or an anion having general formula B(Ar)₄ ⁽⁻⁾ wherein the substituents Ar, equal to or different from each other, are selected from aryl groups.
 5. The catalytic system for the (co)polymerization of conjugated dienes according to claim 4, wherein said co-catalyst (b) is selected from: tri-iso-butyl-aluminum (TIBA), di-iso-butyl-aluminium hydride (DIBAH), methylaluminumoxane (MAO), or tetra-iso-butyl-aluminumoxane (TIBAO).
 6. The catalytic system for the (co)polymerization of conjugated dienes according to claim 4, wherein in said catalytic system the molar ratio between the lanthanide present in the bis-imine pyridine complex of lanthanides (a) having general formula (I) and the aluminium present in the co-catalyst (b) selected from aluminium alkyls (b₁) or aluminumoxanes (b2), ranges from 5 to 5,000.
 7. The catalytic system for the (co)polymerization of conjugated dienes according to claim 4, wherein in said catalytic system the molar ratio between the lanthanide present in the bis-imine pyridine complex of lanthanides (a) having general formula (I) and the boron present in the co-catalyst (b) selected from compounds (b₃) having general formula (IV), ranges from 0.1 to
 15. 8. (canceled)
 9. The catalytic system according to claim 1, wherein said conjugated dienes are 1,3-butadiene, isoprene. 10-12. (canceled) 